Preferred embodiments of the present invention relate to apparatus and methods for computing filter coefficients for an adaptive filter for filtering a microphone signal so as to suppress an echo due to a loudspeaker signal, as may be employed, for example, within the context of conference systems. Examples of conference systems include telephone conference systems, video conference systems or other bi-directional conference systems.
Acoustic echoes arise whenever tones, sounds and noises from a loudspeaker are picked up by a microphone located in the same room or in the same acoustic environment. In telecommunication systems, this acoustic feedback signal is transmitted back to the far-end subscriber, who notices a delayed version of their own speech. In this context, echo signals represent a very distracting disturbance and may even inhibit interactive full-duplex communication. Additionally, acoustic echoes may result in howling effects and other instabilities of the acoustic feedback loop.
WO 2006/111370 A1 relates to a method and an apparatus for removing an echo in a multichannel audio signal. Acoustic echo control and noise suppression are an important part of any hands-free telecommunication system such as telephone, audio or video conference systems. The method, described in the document, of processing multichannel audio loudspeaker signals and at least one microphone signal in this context includes the steps of transforming the input microphone signal to input microphone short-time spectra, computing a combined loudspeaker signal short-time spectrum from the loudspeaker signals, computing a combined microphone signal short-time spectrum from the input microphone signal, estimating a magnitude spectrum or a power spectrum of the echo in the combined microphone signal short-time spectrum, computing a gain filter for magnitude modification of the input microphone short-time spectrum, applying the gain filter to at least one input microphone spectrum, and converting the filtered input microphone spectrum to the time domain.
Echo suppression and echo cancellation systems as are employed today and may also be referred to as echo removal systems in summary, frequently have the problem that they do not cope with different sound, tone and noise components in an optimum manner despite the use of adaptive filters. If one component is predominant as compared to another, a non-optimum suppression of the echo of the loudspeaker signal may occur in the microphone signal of such a communication system, for example. On the other hand, in the case of a deviating composition of the components of the different sources, tonal artifacts may arise due to the utilization of an echo suppression or echo cancellation system, which tonal artifacts are also perceived as extremely annoying.